1. Field of the Invention
The present invention generally relates to a method for forming a printing plate used in a planographic (lithographic) printing operation and the like. More specifically, the present invention is related to such a plate-making method capable of recording a sharp image without being adversely influenced by laser flare, and also applicable to a process operation executed in a light room. Furthermore, the present invention is directed to a plate-making apparatus used in a plate making method, and an image recording material such as a photosensitive plate-making material.
2. Description of the Related Art
While a CTP (computer-to-plate) plate-making system (will be simply referred to as a “CTP system” hereinafter) is employed as an example, conventional techniques of plate-making methods will now be described. This CTP system corresponds to such a system that while image information stored in a computer is recorded on a photosensitive plate-making material by using a laser scanner and the like, the recorded image is developed to form a printing plate. In this CTP system, printing intermediate films with respect to the respective colors employed in the known photolithography process is no longer required. As a result, this CTP system may constitute a considerably attractive system having such various merits, for instance, low cost, high-speed processing, and high image qualities.
Very recently, two different types of photosensitive plate-making materials, namely, 1) high-sensitivity photopolymer plate-making material and 2) thermal photosensitive plate-making material, have been positively developed in this CTP system in conjunction with great progresses of laser light sources used to expose these plate-making materials. In the current CTP systems with employment of the above-explained photosensitive plate-making materials, the below-mentioned problems may occur:
1) One conventional CTP system with employment of the above-explained high-sensitivity photopolymer plate-making material:
Normally, this CTP system employs as exposure light, laser light having power of approximately 100 mW to 200 mW and having wavelengths from UV (ultraviolet) to blue/green, which is produced from either an Ar+ laser or an LD-excited green solid-state laser. This CTP system may have merits of processing/printing aptitude similar to those of the conventional system using the PS (Pre-Sensitized) plate corresponding to the photosensitive plate-making material.
However, in this CTP system, since the laser light having the wavelengths from UV to blue/green and the high sensitive photopolymer are employed, the adverse influences of the laser flares are apt to be caused by laser light scattering phenomenon, laser light reflections, and laser light diffraction, which occurred in the optical system and the photosensitive planes. As a result, the resultant image qualities may be easily deteriorated. Also, in the case that the laser light of blue/green color is employed as the exposure light, both the exposure process and the developing process of the plate are required to be performed in a dark room. Namely, darkroom process operation is required.
2) Another conventional CTP system with employment of the above-described thermal photosensitive plate-making material:
A thermal photosensitive plate-making material is classified into both a thermal/negative photosensitive plate-making material and a thermal/positive photosensitive plate-making material. Since these photosensitive plate-making materials own very low sensitivities, these plate-making materials are not photosensitized by the normal illumination light, although high power laser light in the class of 1 W to low must be irradiated to these very low sensitive plate-making materials. Therefore, these photosensitive plate-making materials can be handled in a light room.
However, since a very large oven is necessarily required in a pre-heat stage with respect to such a thermal/negative photosensitive plate-making material, a processing system thereof becomes bulky. Furthermore, this thermal/negative photosensitive plate-making material owns another problem that a latitude or a permissible range with respect to a heating temperature in a heating stage is narrow, and also very cumbersome temperature controls are necessarily required. On the other hand, in the case that a thermal/positive photosensitive plate-making material is employed in the CTP system, although a heating stage is not required, there is such a problem that a latitude of a developing process is narrow and also very strict management is required with respect to the developing conditions. Further, these two thermal photosensitive plate-making materials own a certain drawback as to stability for a long time period.